I think the wheel was not tightened properly. When the lugs are loose the rim will come off in short order. Most folks think the lugs hold the tire on. Actually the friction between the rim and the brake drum hold the rim on there. The bolts just provide the compression to keep the two surfaces in contact. Bolts clamp two things together. The bolt is not designed to handle shear loads. If the bolts were to tight, you might have one or two bolts that came off. If they were loose like if they did not torque them after getting them snug, then they will come off. You need to talk to whoever put the wheels on.